The present invention relates to a process for removing water from an aqueous solution containing water soluble polymer. More particularly, the present invention relates to a process for recovering water soluble high molecular weight polymer from aqueous gel thereof without deterioration of properties.
Water soluble high molecular weight polymers, especially polymer or copolymer composed mainly of acrylamide, methacrylamide, quaternary ammonium salts of dialkylaminoalkyl acrylate or methacrylate have wide uses as flocculants for various waste waters, chemicals in paper making or textiles, and the like. These water soluble polymers are generally prepared by aqueous polymerization system, that is, polymerizing aqueous monomer solution or aqueous monomer solution emulsified with organic liquid and resulted polymer is dissolved in aqueous solution. Because the polymer solution is normally a viscous or rubbery mass, it is hereinafter termed gel or aqueous polymer gel. To prepare the powder of the polymer, it is necessary to remove water from aqueous polymer gel until the water content being below 10% by weight. Most available industrial methods for removing water from the aqueous polymer gel are heat drying method and azeotropic distillation method. (German Patent Publication No. 14 94 967)
But it had been found that the drying of the aqueous polymer gel by these methods had deleterious effect on the properties of the polymer especially solubility to the water which are important properties for flocculant is reduced. The deterioration formation increased when the polymer is treated under elevated temperature, for example, the temperature higher than 40.degree. C. Inventors of the present invention found that it is useful to add some compounds when drying the aqueous polymer gel for preventing the deterioration of the polymer properties.